It's good to have a lot of time to practice, but then you should divide your time with different things and have proper breaks. If you are not working on very long pieces yet, you don't really need so much time on them at one pactice session. Working too long on one thing is not very productive (the brain gets tired). When you aren't getting better and concentration starts failing, it's little use to continue drilling. Just do it again the next day and often you see improvement right away. That's because much of deeper learning happens after practicing, not during. It doesn't often go like more hours spent on the piano=faster learning.
This is something that I need to tell myself all the time, because I have the tendency to get too absorbed on something difficult and I just cannot stop even if I am not working efficiently anymore.